1. Field of the Invention
This invention relates to a magnetic recording medium capable of preventing adherence of matters to a magnetic head, and a cleaning tape for removing the magnetic head of matters adherent thereto.
2. Description of the Prior Art
In the field of magnetic recording, a demand for long-time recording is intense to meet the high capacity recording especially in the field of data cartridges for hard disk back-up and digital video recorders. The long time recording is achieved after the thickness of a tape has been reduced or the cassette shell has been modified. so that the effective length of tape is increased.
The data cartridge generally achieves recording/replay by the helical scan method. With the helical scan method, however, the magnetic surface of a tape runs so fast past a magnetic head that the head becomes hot while pressed against the running tape, and tends to be inflicted with burned matters thereupon.
If the contact time is lengthened or the scan speed is increased, to achieve long-time recording, it will further enhance the generation/adherence of burned matters onto the surface of the magnetic head.
Particularly, under a hot, humid atmosphere, a magnetic tape presents a reduced abrasion, and thus metal oxides generated tribologically harden by heating, and adhere and accumulate onto the surface of the head without being abraded by the tape. The accumulated burnt matters form a gap (spacing) between the magnetic tape and head, thereby interfering with the communication of signals between them.
Currently, a supercalender treatment is applied to a tape to improve its surface performance, to further increase its electromagnetic conversion and to reduce its spacing loss. This treatment, however, rather enhances the friction between a magnetic tape and magnetic head, which will lead to the increased generation/adherence of burnt matters on the surface of the magnetic head.
To inhibit the generation/adherence of burnt matters onto the magnetic head, a number of trials have been made: a reducing agent such as a derivative from ascorbic acid is added to a magnetic tape as an antioxidant, and a lubricant is added to a tape at a concentration higher than normal to further reduce the surface friction. However, once burnt matters have been generated on the surface of a tape, they stick so firmly thereupon that they are scarcely responsive to those treatments.
Alternatively, a number of methods have been developed to clean a magnetic head of adhered burnt matters: a cleaning tape is introduced to abrade the head physically, and a cleaning roll mechanism is implemented to abrade the magnetic head continuously. For example, Japanese Unexamined Patent Publication No.57-208626 proposes a cleaning tape which is produced after a powder of .alpha.-Al.sub.2 O.sub.3 or Cr.sub.2 O.sub.3 having a Morse hardness of 8 or more has been applied as an abrading agent together with a bonding resin onto a polyester film base.
The abrading particles used for such physical abrasion has such a high hardness that, while being excellent in their abrading activity, they often wear and damage the magnetic head itself while they are cleaning the head of burnt matters. The magnetic head used for recording/replay of 8 mm videotapes or digital videotapes has a gap as small as 0.3 .mu.m or less, and on that gap a tape runs past at a very high speed. Such magnetic head so readily suffer from mechanical impacts that it, if pressed hard against the abrading particles described above, will be worn away or damaged easily.
As a remedy for this problem, Japanese Examined Patent Publication No. 8-00169 5 proposes a method wherein the size of abrading particles is so adjusted as to reduce the wear of a magnetic head. However, the wear of a magnetic head is unavoidable even when the size of abrading particles is adjusted as long as the particles are made of .alpha.-Al.sub.2 O.sub.3 or Cr.sub.2 O.sub.3 or substance high in hardness.
To remove or reduce burnt matters adherent onto a magnetic head, various treatments have been applied to a recording medium or to a cleaning tape, but they do not give satisfactory results, and further studies are needed to meet the problem.